Injector configured for arrangement within a reaction chamber of a substrate processing apparatus

ABSTRACT

The invention relates to an injector configured for arrangement within a reaction chamber of a substrate processing apparatus to inject gas in the reaction chamber. The injector may be elongated along a first axis and configured with an internal gas conduction channel extending along the first axis and provided with at least one gas entrance opening and at least one gas exit opening. The injector may have a width extending along a second axis perpendicular to the first axis substantially larger than a depth of the injector extending along a third axis perpendicular to the first and second axis. The wall of the injector may have a varying thickness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 63/119,216 filed Nov. 30, 2020 titled INJECTOR CONFIGURED FORARRANGEMENT WITHIN A REACTION CHAMBER OF A SUBSTRATE PROCESSINGAPPARATUS, the disclosure of which is hereby incorporated by referencein its entirety.

FIELD

The present invention relates to an injector configured for arrangementwithin a reaction chamber of a substrate processing apparatus to injectgas in the reaction chamber. The injector may be substantially elongatedalong a first axis and configured with an internal gas conductionchannel extending along the first axis and provided with at least onegas entrance opening and at least one gas exit opening. The injector mayhave a width extending along a second axis perpendicular to the firstaxis substantially larger than a depth of the injector extending along athird axis perpendicular to the first and second axis.

BACKGROUND

A substrate processing apparatus such as a vertical furnace forprocessing substrates e.g. semiconductor wafers may include a heatingelement, placed around a bell jar-shaped process tube. The upper end ofthe process tube may be closed, for example by a dome-shaped structure,whereas the lower end surface of the process tube may be open.

The lower end may be partially closed by a flange. An interior boundedby the tube and the flange forms a reaction chamber in which wafers tobe treated may be processed. The flange may be provided with an inletopening for inserting a wafer boat carrying wafers into the reactionchamber. The wafer boat may be placed on a door that is verticallymoveably arranged and that is configured to close off the inlet openingin the flange.

The flange may support one or more injectors to provide a gas to thereaction chamber. For this purpose the injector may be configured withthe internal gas conduction channel. Additionally, a gas exhaust ductmay be provided in the flange. This gas exhaust may be connected to avacuum pump for pumping off gas from the reaction chamber. The gasprovided by the injectors in the reaction chamber may be a reaction(process) gas for a deposition reaction on the wafers. This reaction gasmay also deposit on other surfaces than the wafers, for example it maydeposit in the internal gas conduction channel. Layers created by thesedeposits may cause clogging and or breakage of the injectors.

SUMMARY

Accordingly an improved injector may be required.

In an embodiment there may be provided an injector configured forarrangement within a reaction chamber of a substrate processingapparatus to inject gas in the reaction chamber, the injector beingsubstantially elongated along a first axis and configured with aninternal gas conduction channel extending along the first axis andprovided with at least one gas entrance opening and at least one gasexit opening, and the injector has a width extending along a second axisperpendicular to the first axis substantially larger than a depth of theinjector extending along a third axis perpendicular to the first andsecond axis, wherein the wall of the injector has a varying thickness.

The various embodiments of the invention may be applied separate fromeach other or may be combined. Embodiments of the invention will befurther elucidated in the detailed description with reference to someexamples shown in the figures.

BRIEF DESCRIPTION OF THE FIGURES

It will be appreciated that elements in the figures are illustrated forsimplicity and clarity and have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexaggerated relative to other elements to help improve understanding ofillustrated embodiments of the present disclosure.

FIG. 1 shows a cross-sectional view of a tube of a vertical furnaceincluding an injector;

FIG. 2 shows a schematic top view of the tube of FIG. 1;

FIG. 3 shows a cross-section of an injector according to an embodimentfor use in the vertical furnace of FIGS. 1 and 2;

FIGS. 4a to 4e schematically show injectors according to anotherembodiment for use in the vertical furnaces of FIG. 1; and,

FIG. 5 depicts the injectors of FIGS. 4a to 4e arranged in a tube.

DETAILED DESCRIPTION

In this application similar or corresponding features are denoted bysimilar or corresponding reference signs. The description of the variousembodiments is not limited to the examples shown in the figures and thereference number used in the detailed description and the claims are notintended to limit what is described to the examples shown in thefigures.

FIG. 1 shows a cross-sectional view of a vertical furnace. The verticalfurnace may comprise a process tube 12 forming a reaction chamber and aheater H configured to heat the reaction chamber. A liner 2 may beprovided along the process tube 12, the liner 2 may comprise asubstantially cylindrical wall delimited by a liner opening at a lowerend and a dome shape top closure 2 d at the higher end.

A flange 3 may be provided to at least partially close the opening ofthe process tube 12. A vertically movably arranged door 14 may beconfigured to close off a central inlet opening O in the flange 3 andmay be configured to support a wafer boat B that is configured to holdsubstrates W. The door 14 may be provided with a pedestal R. Thepedestal R may be rotated to have the wafer boat B in the reactionchamber rotating.

In the example shown in FIG. 1, the liner 2 may comprise a substantialcylindrical liner wall having an outer substantial cylindrical surface 2a and an inner substantial cylindrical surface 2 b. The flange 3 may beconfigured to at least partially close the tube opening and the lineropening defined more precisely by the lower end surface 2 c of the liner2. The flange 3 comprises:

an inlet opening O configured to insert and remove the boat B configuredto carry substrates W in the reaction chamber I of the liner 2;

a gas inlet 16 to provide a gas F, for example a process gas to thereaction chamber I; and,

a gas exhaust duct 7 to remove gas from the reaction chamber I.

The substrate processing apparatus may have a vessel for containingsilicon precursors and may be operably connected to an elongatedinjector 17 via the gas inlet 16. The injector 17 may be constructed andarranged to extend vertically into the reaction chamber I along thesubstantial cylindrical wall of the liner 2 towards a higher second end.The injector may be supported by the flange 3 at a lower first end ofthe injector and may comprising an injector opening to inject gas in thereaction chamber. One or more injectors 17 may be used to provide theprocess gas to the reaction chamber I. One injector 17 is shown in FIG.2.

Gas exhaust duct 7 for removing gas from the reaction chamber I may beconstructed and arranged below the injector opening 18. In this way adown flow F in the reaction chamber of the liner 2 may be created. Thisdown flow F may transport contamination of reaction byproducts andparticles from the substrate W, the boat B, the liner 2 and/or thesupport flange 3 downward to the exhaust duct 7 away from the processedsubstrates W.

The gas exhaust duct 7 for removing gas from the reaction chamber I maybe provided below the liner opening of the liner 2. This may bebeneficial since a source of contamination of the reaction chamber maybe formed by the contact between the liner 2 and the flange 3. Again,the down flow F may transport the particles from the liner-flangeinterface downward to the exhaust away from the processed substrates.

The gas exhaust openings 8 may be constructed and arranged between theliner 2 and the flange 3 for removing gas from the circumferential spacebetween the liner 2 and the tube 12. In this way the pressure in thecircumferential space and the interior space I may be made equal and ina low pressure vertical furnace may be made lower than the surroundingatmospheric pressure surrounding the tube 12. The vertical furnace maybe provided with a pressure control system to remove gas from thereaction chamber.

In this way the liner 2 may be made rather thin and of a relatively weakmaterial since it doesn't have to compensate for atmospheric pressure.This creates a larger freedom in choosing the material for the liner 2.The thermal expansion of the material of liner 2 may be chosen such thatit may be comparable with the material deposited on the substrate in thereaction chamber. The latter having the advantage that the expansion ofthe liner and the material deposited also on the liner may be the same.The latter minimizes the risk of the deposited material dropping of as aresult of temperature changes of the liner 2.

The tube 12 may be made rather thick and of a relatively strongcompressive strength material since it may have to compensate foratmospheric pressure with respect to the low pressure on the inside ofthe tube. For example, the low pressure process tube 12 can be made of 5to 8, preferably around 6 mm thick Quartz. Quartz has a very lowCoefficient of Thermal Expansion (CTE) of 0.59×10−6 K−1 (see table 1)which makes it more easy to cope with thermal fluctuations in theapparatus. Although the CTE of the deposited materials may be higher(e.g., CTE of Si3N4=3×10−6 K−1, CTE of Si=2.3×10−6 K−1) the differencesmay be relatively small. When films are deposited onto tube made ofquartz, they may adhere even when the tube goes through many largethermal cycles however the risk of contamination may be increasing.

The liner 2 may circumvent any deposition on the inside of the tube 2and therefore the risk of deposition on the tube 12 dropping off may bealleviated. The tube may therefore be made from Quartz.

A liner 2 of silicon carbide (CTE of SiC=4×10−6 K−1) may provide an evenbetter match in CTE between deposited film and liner, resulting in agreater cumulative thickness before removal of the deposited film fromthe liner may be required. Mismatches in CTE result in cracking of thedeposited film and flaking off, and correspondingly high particlecounts, which is undesirable and may be alleviated by using a SIC liner2. The same mechanism may work for the injector 17 however for injectors17 it may be the case that the injector may be breaking if too muchmaterial with different thermal expansion is deposited. It may thereforebe advantageously to manufacture the injector 17 from silicon carbide orsilicon.

TABLE 1 Coefficient of Thermal Expansion (CTE) of Materials inSemiconductor Processing Material Thermal expansion (ppm/K) Quartz 0.59Silicon nitride 3 Silicon 2.3 Silicon carbide 4.0 Tungsten 4.5

Whether a material is suitable for the liner 2 and or the injector 17may be dependent on the material that is deposited. It is thereforeadvantageously to be able to use material with substantially the samethermal expansion for the deposited material as for the liner 2 and/orthe injector 17. It may therefore be advantageously to be able to usematerial with a thermal expansion for the liner 2 and/or the injector 17relatively higher than that of quartz. For example Silicon Carbide SiCmay be used. The silicon carbide liner may be between 4 to 6, preferably5 mm thick since it doesn't have to compensate for atmospheric pressure.Pressure compensation may be done with the tube.

For systems depositing metal and metal compound materials with a CTEbetween about 4×10−6 K−1 and 6×10−6 K−1, such as TaN, HfO2 and TaO5, theliner and injector materials preferably may have a CTE between about4×10−6 K−1 and 9×10−6 K−1, including, e.g., silicon carbide.

For deposition of material with even a higher CTE, the liner and/orinjector materials may be chosen as for example depicted by table 2.

TABLE 2 Coefficient of Thermal Expansion (CTE) of Ceramic ConstructionMaterials Material Thermal expansion (ppm/K) Macor 12.6 Boron Nitride11.9 Glass, ordinary 9 Mullite 5.4

Within the tube 12 a purge gas inlet 19 may be provided for providing apurge gas P to the circumferential space S between an outer surface ofthe liner 2 b and the process tube 12. The purge gas inlet comprises apurge gas injector 20 extending vertically along the outer surface ofthe cylindrical wall of the liner 2 from the flange 3 towards the topend of the liner. The purge gas P to the circumferential space S maycreate a flow in the gas exhaust openings 8 and counteract diffusion ofprocess gas from the exhaust tube 7 to the circumferential space S asdepicted by the arrows.

The flange 3 may have an upper surface. The liner 2 may be supported bysupport members 4 that may be connected to the outer cylindrical surfaceof the liner wall 2 a and each have a downwardly directed supportingsurface. The liner may also be supported directly on the upper surfaceof the flange 3 with it lower surface 2 c, while allowing a gas exhaustopening 8 between the upper surface and the liner 2.

The supporting surfaces of the support members 4 may be positionedradially outwardly from the inner cylindrical surface 2 b of the liner2. In this example, the supporting surfaces of the supporting members 4may be also positioned radially outwardly from the outer cylindricalsurface 2 a of the liner 2 to which they are attached. The downwardlydirected supporting surface of the support members 4 may be in contactwith the upper surface of the flange 3 and support the liner 2 whileallowing a gas exhaust opening 8 between the upper surface and the liner2.

The support flange 3 of the closure may include gas exhaust openings 8to remove gas from the reaction chamber of the liner 2 and the circularspaces between the liner 2 and the low pressure tube 12. At least someof the gas exhaust 8 openings may be provided between the upper surfaceof the flange 3 and the liner 2. At least some of the gas exhaustopenings may be provided near the liner opening. The gas exhaustopenings 8 may be in fluid connection with a pump via exhaust duct 7 forwithdrawing gas from the reaction chamber and the circumferential spacebetween the process tube 12 and the liner 2.

FIG. 2 is a schematic top view of the tube of FIG. 1. The figure showsthe liner 2 with the cylindrical wall defining an inner substantiallycylindrical surface 2 b and an outer substantially cylindrical surface 2a that form an opening 13 for inserting a boat configured to carrysubstrates.

Also visible are the support members 4. In this example, the liner 2 hasthree support members 4 that are equally spaced along the circumferenceof the outer cylindrical surface 2 a of the liner 2. The flange may beprovided with positioning projections 5 that extend upwards from theupper surface 3 a of the flange. The positioning projections 5 mayengage the support members 4 on a tangential end surface thereof. As aresult, the positioning projections 5 have a centering function for theliner 2 relative to the support flange 3.

The liner 2 and the notches forming the support members 4 may bemanufactured from quartz, silicon or silicon carbide. The liner 2delimiting the reaction chamber may have a radially outwardly extendingbulge 2 e to accommodate the injector 17 or a temperature measurementsystem in the reaction chamber.

FIG. 3 schematically shows a cross section of an injector 17 accordingto an embodiment for use in the vertical furnace of FIGS. 1 and 2. Theinjector 17 may be configured for arrangement within a reactor of avertical furnace to inject gas in the reaction chamber I. The injector17 may be configured with an internal gas conduction channel 20 totransport gas. The injector 17 may be substantial elongated along afirst axis and the internal gas conduction channel 20 may extend alongthe first axis.

The injector 17 may have a width extending along a second axis Xperpendicular to the first axis substantially larger than a depth of theinjector extending along a third axis Y perpendicular to the first andsecond axis. The wall 22 of the injector 17 may have a varyingthickness. The wall 22 of the injector 17 may have a varying thicknessalong the second axis X. The varying thickness of the wall 22 may varybetween 10 to 60%. For example with 40% as depicted from 2.5 to 3.5 mm.

The internal gas conduction channel 20 of the injector 17 may have asubstantially oval shaped cross section. The internal gas conductionchannel 20 may extend along its width in the second axis X substantiallylarger than it extends along its depth in the third axis Y. Thesubstantially oval shaped cross section may be build up out of aplurality of circles with a fixed radius to accommodate drilling andmilling. Rounded corners also avoid the build-up of stress andcontamination in the corners. The radius of the circles may be 1 to 10mm, for example a circle having a radius of 5 mm. The horizontal innercross-section area of the internal gas conduction channel 20 inside theinjector 17 may be between 100 and 1500 mm², preferably between 200 and500 mm² and most preferably between 250 and 350 mm².

The substantially oval shaped gas conduction channel 20 may be partiallypinched off in the middle. Whereby pinched off means that the internalgas conduction channel 20 has a smaller depth in the third direction.The middle refers to the middle with respect to the width of theinjector 17 in the second direction X. Pinching off may be accomplishedby the wall 22 having the varying thickness. For example, by the 22 wallhaving an increased thickness in the middle of its width which pinchesof the gas conduction channel 20.

The substantially oval shaped gas conduction channel 20 may be partiallypinched off in the middle of the second direction by a bulb 24 makingthe wall 22 thicker and extending into and pinching off the gasconduction channel 20. The surface of the bulb 24 may be partiallyfollowing a bulb circle. The bulb circle may have a constant radius withrespect to an axis parallel to the first axis. The radius may be between10 to 50 mm, preferably between 15 and 30 mm and as depicted it may be23 mm.

The wall 22 of the injector 17 may have a varying thickness along thethird axis Y. The varying thickness along the third axis Y may berelatively small variation around 7 mm.

The wall 22 of the injector 17 may have a varying thickness over itscircumference along the second and third axis X, Y. The varyingthickness of the wall 22 may vary between 4 to 60%.

The wall 22 of the injector 17 may have has a varying thickness along asubstantial part of the first axis. In this way strength may be addedwhere it is necessary.

The injector 17 may have a gas exit opening 25. The gas exit opening 25may have a radius of 3 to 15 mm, preferably between 4 to 10 mm and mostpreferably between 5 and 9 mm, for example 8 mm.

FIGS. 4a to 4e schematically show injectors 17 a, b, c according toanother embodiment for use in the vertical furnace of FIGS. 1 and 5. Theinjectors 17 a, b, c of FIGS. 4a to 4e each may be specially configuredto provide process gas at a particular height in the reaction chamber I.The injectors 17 a, b, c of FIGS. 4a to 4e may therefore be optimized tocooperate together as depicted in FIG. 5. Alternatively, each injector17 may be used singularly as depicted in FIG. 2. The injectors 17 a, b,c may be substantially elongated along a first axis Z.

The injectors 17 a, b, c may be configured with an internal gasconduction channel 20 to transport process gas. The internal gasconduction channel 20 may extend along the first axis Z. The internalgas conduction channel 20 of the injector 17 a, b, c may have asubstantially oval shaped cross section.

The internal gas conduction channel 20 may extend along the second axisX between 10 to 50 mm, preferably between 20 and 30 mm, for exampleabout 25 mm. The internal gas conduction channel 20 may extend along thesecond axis X substantially larger than the channel extends along thethird axis Y. The internal gas conduction channel 20 may extend alongthe third axis Y between 8 to 30 mm, preferably between 10 and 20 mm,for example about 12 mm.

The substantially oval shaped cross section may be built up out ofcircles with a radius of 1 to 10 mm, for example a circle having aradius of 5 mm. This avoids straight corners in the gas conductionchannel 20 because the corners then will have a minimal roundness of 1to 10 mm for example 5 mm.

The horizontal inner cross-section area of the internal gas conductionchannel 20 inside the injector 17 may be between 100 and 1500 mm²,preferably between 200 and 500 mm² and most preferably between 250 and350 mm².

The substantially oval shaped gas conduction channel 20 may be partiallypinched off in the middle. Whereby pinched off means that the internalgas conduction channel 20 is smaller in the third direction Y. Themiddle refers to the middle with respect to the width of the injectors17 a, b, c in the second direction X. Pinching off may be accomplishedby the 22 wall having an increased thickness in the middle.

The substantially oval shaped gas conduction channel 20 may be partiallypinched off in the middle of the second direction by a bulb 24 providedto the wall 22 and extending into the gas conduction channel 20. Thesurface of the bulb 24 may be partially following a circle. The circlemay have a constant radius with respect to an axis parallel to the firstaxis. The radius may be between 10 to 50 mm, preferably between 15 and30 mm and as depicted it may be 23 mm.

The injectors 17 a, b, c may have a width extending along a second axisX perpendicular to the first axis substantially larger than a depth ofthe injector extending along a third axis Y perpendicular to the firstand second axis as depicted in FIG. 4c . The wall 22 of the injectors 17a, b, c may have a varying thickness.

The wall 22 of the injectors 17 a, b, c may have a varying thicknessalong the third axis Y. The wall 22 of the injectors 17 a, b, c may havea varying thickness over its circumference along the second and thirdaxis X, Y. The wall 22 of the injectors 17 a, b, c may have a varyingthickness along a substantial part of the first axis X.

The injectors 17 a, b may be so called multi hole injectors and have aplurality of gas exit holes 25 along their length in the direction ofthe second end 23 opposite to the first end 21 as depicted in FIG. 4aand b. The gas exit opening 25 may have a radius of 3 to 15 mm,preferably between 4 to 10 mm and most preferably between 5 and 9 mm,for example 6 mm. The longer injector 17 a of the plurality of injectors17 a, b, c may have multiple gas exit holes 25 as depicted in FIG. 4aand may extend within the interior to close to the top closure 2 d(FIGS. 1 and 5) of the closed liner 2. The shorter injector 17 b of theplurality of injectors 17 a, b, c may have multiple gas exit holes 25 asdepicted in FIG. 4b and extend to the middle of the boat B.

The size of the gas conduction channel 20 may be smaller at the firstend 21 where the injectors 17 a, b, c may connect to the gas inlet 16near the flange 3. Since the temperature is lower near the first end 21less process gas is deposited in the internal channel 20 near the firstend 21.

The depth of the injectors 17 a, b, c in the third direction Y may bedecreasing towards the second end 23. The injector which extends withinthe interior Ito close to a top closure 2 d of the closed liner 2 mayhave a shape with a dimension in a direction in a radial direction whichis decreasing closer to the top closure in FIG. 1.

The injectors 17 a, b, c of FIGS. 4a to 4e each may be speciallyconfigured to provide process gas at a particular height in the reactionchamber I. At least one of the injectors 17 a, b, c may therefore have adifferent length.

The longer injectors 17 a, c of the plurality of injectors 17 asdepicted in FIGS. 4a and 4e may extend within the interior Ito close tothe top closure 2 d of the closed liner 2 as depicted in FIGS. 1 and 5.The longer injector 17 c of the plurality of injectors 17 a, b, c mayhave a single gas exit hole 25 at the second end 23 as depicted in FIG.4d . This injector may be called a dump injector 17 c which is closedalong its elongated length to have only one single process gas exit atits second end 23. FIG. 4e depicts the cross section of this dumpinjector which has the same properties as described in relation to FIG.4c above except that there is no gas exit hole 25 on the side.

The single gas exit hole 25 at the second end 23 of the dump injectormay have the same properties as described in relation to FIG. 4c above.The single gas exit hole 25 of the dump injector may be between 100 and1500 mm², preferably between 200 and 500 mm² and most preferably between250 and 350 mm². The injectors 17 a, b, c of FIGS. 4a to 4e maytherefore be optimized to cooperate together as depicted in FIG. 5.

FIG. 5 depicts how the injectors 17 a, b, c of FIGS. 4a to 4e may bearranged in a tube 2. The injector 17 a, b may be the multiholeinjectors (see FIG. 4a and b ) provided with a series of exit openings25 extending in the elongated direction along the injector 17 a, b totransport gas out of the conduction channel into the reaction chamber I.The shorter injector 17 b and/or the longer injector 17 a of theplurality of injectors 17 a, b, c may have multiple gas exit holes 25.The exit openings 25 may be substantially round. The series of exitopenings 25 may be aligned along a line over the surface of themultihole injectors 17 a, b.

The exit openings 25 may be configured such that gas is injected in atleast two different directions substantially perpendicular to theelongated direction of the multi hole injector so as to improve mixingof the process gas in the reaction chamber I. The series of openings 25may therefore be aligned along at least two lines over the surface ofthe injector 17. Whereas a first line with openings may be shown inFIGS. 4a and b a similar second line with openings 25 may be configuredon the other side of the injector 17 as depicted in FIG. 5. The seriesof openings 25 along a first line may be configured such that gas isinjected in a first direction and the series of openings 25 along asecond line may be configured such that gas is injected in a seconddirection. The first and second direction may be under an angle between30 to 180 degrees with each other.

Exit openings 25 may be provided pair-wise at the same height asdepicted in FIG. 5. Alternatively, the exit openings 25 may be providedpair-wise at unequal height to improve the strength of the injector 17.The two exit openings may inject the gas in two directions, for exampleunder an angle of about 90 degrees, to improve the radial uniformity.

The distance between the openings 25 of the series of openings may beconstant when going from the first end 21 to the second end 23 of themultihole injector 17 in FIG. 4a and b. Advantageously each exit opening25 may have a substantial equal flow of process gas through the exitopening 25.

The distance between the exit openings 25 of the series of exit openingsmay also be designed such that it decreases when going from the firstend 21 to the second end 23 of the multihole injector 17. The later maybe beneficial to compensate for pressure loss when the processing gas istransported from the first end 21 to the second end 23.

The area of the exit openings for multihole injectors may be between 1to 200 mm², preferably between 7 to 100 mm², more preferably between 13and 80 mm². Larger openings may have the advantage that it takes longerfor the openings to clog because of deposited layers within theopenings. The number of exit openings 25 may be between 2 and 40,preferably 3 and 30, and more preferably 5 and 15.

The longer injector 17 c of the plurality of injectors 17 a, b, c mayhave a single gas exit hole at the second end as depicted in FIG. 4d .This injector 17 c may be called a dump injector 17 c which is closedalong its elongated length to have only one single process gas exit atits second end near the top closure 2 d of the liner. The single gasexit hole at the second end of the dump injector may have the sameproperties as described in relation to FIG. 4d, e above.

The exit opening 25 of the gas injector 17 may be configured to reduceclogging of the opening. The exit opening may have a concave shape fromthe inside to the outside. The concave shape with the surface area ofthe opening on a surface on the inside of the injector larger than thesurface area of the exit opening 25 on the outside of the injector mayreduce clogging. The larger area on the inside allows more deposition atthe inner side where the pressure and therefore the deposition islarger. On the outside the pressure is reduced and therefore thedeposition is also slower and a smaller area may collect the samedeposition as a larger diameter on the inside.

Reducing the pressure with the injector may result in a reduction of thereaction rate within the injector 17 because the reaction rate typicallyincreases with increasing pressure. An additional advantage of a lowpressure inside the injector is that gas volume through the injectorexpands at low pressure and for a constant flow of source gas theresidence time of the source gas inside the injector reducescorrespondingly. Because of the combination of both, the decompositionof the source gases may be reduced and thereby deposition within theinjector may be reduced as well.

The process gas that may be injected via the injector 17 in the reactionchamber I to deposit layers on the wafers W in the wafer boat B may alsodeposit on the internal gas conduction channel or on the outer surfaceof the injector 17. This deposition may cause tensile or compressivestress in the injector 17. This stress may cause the injector 17 tobreak which causes down time of the vertical furnace and/or damage tothe wafers W. Less deposition within the injector therefore may prolongthe lifetime of the injector 17 and make the vertical furnace moreeconomical.

Temperature changes of the injector 17 may even increase these stresses.To alleviate the stress the injector may be made from a material whichmay have the coefficient of thermal expansion of the material depositedwith the process gas. For example, the gas injector may be made fromsilicon nitride if silicon nitride is deposited, from silicon if siliconis deposited or from silicon oxide when silicon oxide is deposited bythe process gas. The thermal expansion of the deposited layer within theinjector may therefore better match the thermal expansion of theinjector, decreasing the chance that the gas injector may break duringchanges of temperature.

Silicon carbide may also be a suitable material for the injector 17.Silicon carbide has a thermal expansion which may match many depositedmaterials.

A disadvantage of a low pressure inside the injector is that theconduction of the injector decreases significantly. This would lead to apoor distribution of the flow of source gas over the opening patternover the length of the injector: the majority of source gas will flowout of the holes near the inlet end of the injector.

To facilitate the flow of process gas inside the injector, along thelength direction of the injector, the injector may be provided with aninternal gas conduction channel with a large inner cross section. Inorder to be able to accommodate the injector according to the inventioninside the reaction chamber, the tangential size of the injector 17 maybe larger than the radial size and the liner 2 may be provided with anoutwardly extending bulge to accommodate the injector.

In an embodiment the two source gases, providing the two constitutingelements of the binary film, are mixed in the gas supply system prior toentering the injector. This is the easiest way to ensure a homogeneouscomposition of the injected gas over the length of the boat. However,this is not essential. Alternatively, the two different source gases canbe injected via separate injectors and mixed after injection in thereaction chamber.

The use of two injector branches allows some tuning possibilities. Whengas of substantially the same composition is supplied to both parts ofthe injector, via separate source gas supply, the flows supplied to thedifferent injector branches can be chosen different to fine-tune theuniformity in deposition rate over the boat. It is also possible tosupply gas of different composition to the two lines of the injector tofine-tune the composition of the binary film over the boat. However, thebest results may be achieved when the composition of the injected gaswas the same for both injector lines.

Since the injector 17 may be supported at its first end 21 by the flange3 the injector 17 may wiggle a little bit at its second end 23 becauseit is a very long and thin structure as depicted in FIG. 1. It istherefore desirable or necessary to design the liner 2, injector 17 andthe wafer boat B so that there is enough space between the three.

An outer side wall of the injector 17 may be tapered towards the secondend 23 of the injector over at least 10%, preferably 30%, morepreferably 50%, and even more preferable over 100% of its length. Byhaving the injector 17 tapered at the second end 23 it may occupy lessspace in the small space between the liner 2 and the wafer boat in thereaction chamber I near its second end 23 where the tolerances are thetightest. The tolerances at which the injector 17 with its taperedsecond end 23 may be positioned in the small space may therefore be abit more relaxed.

The injector extending within the interior to close to a top closure ofthe closed liner may therefore have a shape with a dimension in adirection in a radial direction which is decreasing closer to the topclosure. Also in vertical furnaces where no liner 2 is used an injector17 with a tapered shape at its second end 23 may be useful in relaxingthe tolerances of positioning the injector in between the tube and theboat.

The injector 17 may comprise multiple branches, for example twobranches, each provided with a separate gas feed conduit connection. Onebranch may inject process gas into the lower part of the reactionchamber and the other branch injects process gas into the upper part ofthe reaction chamber. The branches may be connected by connecting parts.However, it is not essential for the invention that the injectorcomprises two or more injector branches. The branches may be partiallytapered at their second end.

The injector 17 may be manufactured from ceramics. The ceramics may beselected from siliconcarbide (SiC), siliconoxide (SiOx), silicon, oraluminumoxide (AlOx). The injectors may be manufactured in a process inwhich first the injector is formed and secondly the injector is baked toharden the ceramics.

Preceramic polymers may be used as precursors which may form the ceramicproduct through pyrolysis at temperatures in the range 1000-1100° C.Precursor materials to obtain silicon carbide in such a manner mayinclude polycarbosilanes, poly(methylsilyne) and polysilazanes. Siliconcarbide materials obtained through the pyrolysis of preceramic polymersmay be known as polymer derived ceramics or PDCs.

Pyrolysis of preceramic polymers is most often conducted under an inertatmosphere at relatively low temperatures. The pyrolysis method isadvantageous because the polymer can be formed into various shapes priorto pyrolysis into the ceramic siliconcarbide. Prior to pyrolysis thematerial is much softer and therefore easier to be shaped in a form.

The injector 17 may comprise a bottom portion connected to a top portionwherein the top portion may be slightly tapered and ends at the secondend 23. The bottom portion may be between 30 and 40 cm long startingfrom the first end 21 and may be substantially straight.

The bottom portion may be provided with a connection pipe 27 (see FIG.4a, b ). The connection pipe 27 may be fitted in a hole in the flange 3(in FIG. 1) to position and hold the injector 17. Such a construction onthe first end 21 of the injector may be advantageously if the injectoris heated because it allows for expansion of the injector 17. Adisadvantage may be that it allows for some wiggling of the injector 17especially at the second end 23.

By having the second end 23 tapered the tolerance for wiggling of theinjector 17 may be increased. The top portion may have a cross sectionalarea at the second end 23 that is 1 to 80%, preferably 3 to 40%, andmost preferably 4 to 20% smaller than the cross sectional area at thefirst end. The top portion may have a wall thickness at the second endthat is 2 to 50%, preferably 5 to 30% and most preferably 10 to 20% thanthe wall thickness at the first end 21.

The injector 17 may have a cross sectional area at the second end thatis 1 to 80%, preferably 3 to 40%, and most preferably 4 to 20% smallerthan the cross sectional area at the first end. The injector may have awall thickness at the second end 23 that is 2 to 50%, preferably 5 to30% and most preferably 10 to 20% smaller than the wall thickness at thefirst end 21.

While specific embodiments have been described above, it will beappreciated that the invention may be practiced otherwise than asdescribed. The descriptions above are intended to be illustrative, notlimiting. Thus, it will be apparent to one skilled in the art thatmodifications may be made to the invention as described in the foregoingwithout departing from the scope of the claims set out below. Variousembodiments may be applied in combination or may be appliedindependently from one another.

What is claimed is:
 1. An injector configured for arrangement within areaction chamber of a substrate processing apparatus to inject gas inthe reaction chamber, the injector being substantially elongated along afirst axis and configured with an internal gas conduction channelextending along the first axis and provided with at least one gasentrance opening and at least one gas exit opening, and the injector hasa width extending along a second axis perpendicular to the first axissubstantially larger than a depth of the injector extending along athird axis perpendicular to the first and second axis, wherein the wallof the injector has a varying thickness.
 2. The injector according toclaim 1, wherein the wall of the injector has a varying thickness alongthe second axis.
 3. The injector according to claim 1, wherein the wallof the injector has a varying thickness along the third axis.
 4. Theinjector according to claim 1, wherein the wall of the injector has avarying thickness over its circumference along the second and thirdaxis.
 5. The injector according to claim 1, wherein the wall of theinjector has a varying thickness along a substantial part of the firstaxis.
 6. The injector according to claim 1, wherein the internal gasconduction channel has a substantially oval shaped cross section wherebythe internal gas conduction channel extends along the second axissubstantially larger than the internal gas conduction channel extendsalong the third axis, wherein the substantially oval shaped crosssection is partially pinched off in the middle of the second directionby the wall having an increased thickness.
 7. The injector according toclaim 6, wherein the substantially oval shaped cross section ispartially pinched off in the middle of the second direction by a bulbprovided to the wall and extending into the internal gas conductionchannel.
 8. The injector according to claim 7, wherein the surface ofthe bulb is partially following a circle, the circle shape having aconstant radius with respect to an axis parallel to the first axis. 9.The injector according to claim 1, wherein the injector has one gasentrance opening at a first end of the injector.
 10. The injectoraccording to claim 9, wherein the injector has a single gas exit openingat the second end, opposite to the first end.
 11. The injector accordingto claim 9, wherein the injector has a plurality of gas exit holes alongits length in the direction of the second end, opposite to the firstend.
 12. The injector according to claim 1, wherein the depth of theinjector in the third direction is decreasing towards the second end.13. The injector according to claim 1, wherein the horizontal innercross-section area of the internal gas conduction channel inside theinjector is between 100 and 1500 mm².
 14. A substrate processingapparatus comprising: a tube; a closed liner configured to extend in theinterior of the tube; a gas injector to provide a gas to an interior ofthe tube; and, a gas exhaust duct to remove gas from the interior,whereby the closed liner comprises: a substantially cylindrical walldelimited by a liner opening at a lower end, a top closure at a higherend, and being substantially closed for gases above the liner opening,wherein the gas injector is a gas injector according to claim
 1. 15. Thesubstrate processing apparatus according to claim 14, wherein theapparatus comprises a plurality of injectors and at least one of theinjectors has a different length.
 16. The substrate processing apparatusaccording to claim 15, wherein the longest of the plurality of injectorsextends within the interior to close to the top closure of the closedliner.
 17. The substrate processing apparatus according to claim 15,wherein one of the longest of the plurality of injectors has a singlegas exit hole.
 18. The substrate processing apparatus according to claim15, wherein one of the longest of the plurality of injectors has aplurality of gas exit holes.
 19. The substrate processing apparatusaccording to claim 15, wherein the shortest of the plurality ofinjectors has a plurality of gas exit hole.
 20. The substrate processingapparatus according to claim 14, wherein the liner is substantiallycylindrical and the horizontal inner cross-section area of the internalgas conduction channel inside the injector has a shape with a dimensionin a tangential direction to the circumference of the substantiallycylindrical liner which is larger than a dimension in a radialdirection.
 21. The substrate processing apparatus according to claim 20,wherein the injector extends within the interior to close to a topclosure of the closed liner and has a shape with a dimension in adirection in a radial direction which is decreasing closer to the topclosure.
 22. The substrate processing apparatus according to claim 14,wherein the liner is supported on a flange and a gas exhaust opening isconstructed and arranged between the liner and the flange for removinggas from the circumferential space between the liner and the tube to thegas exhaust duct.